Rotary machines include, without limitation, turbines for steam turbines and compressors and turbines for gas turbines. A steam turbine has a steam path which typically includes, in serial-flow relationship, a steam inlet, a turbine, and a steam outlet. A gas turbine has a gas path which typically includes, in serial-flow relationship, an air intake (or inlet), a compressor, a combustor, a turbine, and a gas outlet (or exhaust nozzle). Gas or steam leakage, either out of the gas or steam path or into the gas or steam path, from an area of higher pressure to an area of lower pressure, is generally undesirable. For example, gas-path leakage in the turbine or compressor area of a gas turbine, between the rotor of the turbine or compressor and the circumferentially surrounding turbine or compressor casing, will lower the efficiency of the gas turbine leading to increased fuel costs. Also, steam-path leakage in the turbine area of a steam turbine, between the rotor of the turbine and the circumferentially surrounding casing, will lower the efficiency of the steam turbine leading to increased fuel costs.
It is known to position variable-clearance labyrinth-seal segments in a circumferential array between the rotor of the turbine and the circumferentially surrounding casing to minimize steam-path leakage. The ends of coil springs engage circumferentially-opposing and generally-matching holes in circumferentially-adjacent seal segments. The coil springs circumferentially urge apart circumferentially-adjacent seal segments. Such circumferentially-urging-apart causes the seal segments to move radially outward within a channel in the casing. This prevents damage to the labyrinth-seal teeth from transient radial movement of the rotor during turbine startup. As the rotor reaches steady-state operating conditions, steam pressure builds up in the turbine, and such pressurized fluid enters the channel and pushes the seal segments radially inward such that the labyrinth-seal teeth are in close proximity to the rotor for more efficient sealing. Designs have been proposed which add brush-seal bristles to a labyrinth seal segment.